CN-122006627-A - Microwave-assisted supercritical fluid rotating bed devolatilization device and method for polypropylene carbonate

CN122006627ACN 122006627 ACN122006627 ACN 122006627ACN-122006627-A

Abstract

The invention discloses a microwave-assisted supercritical fluid rotating bed devolatilization device and method for polypropylene carbonate, and relates to the technical field of polymer processing. The device comprises a horizontal high-pressure closed kettle body, a magnetic coupling driving system, a microwave heating system and a wave-transparent rotary drum. The method adopts a multi-period variable-pressure circulation process of 'boosting swelling-pressure maintaining microwave heating-rapid depressurization' while keeping the continuous rotation of the roller to prevent the adhesion of materials. The invention uses supercritical carbon dioxide plasticization to reduce mass transfer resistance, uses microwaves to selectively heat polar impurities to overcome desorption energy barriers, forms pressure difference inside and outside particles by periodical pressure rising and reducing to promote deep impurity diffusion, and maintains mass transfer driving force by gas phase displacement. The invention can realize deep devolatilization of the polypropylene carbonate at the low temperature of 35-60 ℃ and effectively avoid thermal degradation and material agglomeration.

Inventors

XI ZHENHAO
ZHAO LING
Guo Dengjian
QIU XIAOYI
HUANG HUAN
WANG XUESONG

Assignees

华东理工大学

Dates

Publication Date: 20260512
Application Date: 20260413

Claims (10)

1. A microwave-assisted supercritical fluid rotating bed devolatilization apparatus for polypropylene carbonate, comprising: the high-pressure airtight kettle body (6) is of a horizontal structure, a constant-temperature heating jacket is arranged outside the kettle body and used for maintaining the basic process temperature in the kettle body, an openable flange end cover is arranged at one end of the kettle body, a side-in type mounting interface is arranged at the other end of the kettle body, an air inlet valve (17) is arranged at the bottom of the kettle body, an air outlet valve (13) is arranged at the top of the kettle body, and a pressure sensor (10) and a temperature sensor (11) which are used for monitoring the state in the kettle in real time are also arranged on the kettle body; The magnetic coupling driving system is arranged at a side-in type mounting interface of a high-pressure airtight kettle body (6) and comprises a variable frequency motor (1), an outer magnetic rotor (2), a sealing isolation cover (3) and an inner magnetic rotor (4), wherein the sealing isolation cover (3) is fixed on the kettle body to form static sealing, the inner magnetic rotor (4) is positioned in the sealing isolation cover (3) and is connected with a stirring main shaft (5), and the outer magnetic rotor (2) is positioned outside the sealing isolation cover (3) and is connected with the variable frequency motor (1) to drive the inner magnetic rotor (4) and the stirring main shaft (5) to rotate under the magnetic coupling effect; The microwave heating system comprises a microwave generator (7), a rectangular waveguide (8) and a high-pressure-resistant wave-transparent window (9) arranged at the top of the kettle body, wherein microwave energy generated by the microwave generator (7) is transmitted through the rectangular waveguide (8) and enters the high-pressure closed kettle body (6) through the high-pressure-resistant wave-transparent window (9), and The wave-transparent rotary component is arranged in the high-pressure airtight kettle body (6) and connected with the stirring main shaft (5), and comprises a wave-transparent rotary roller (16) and a lifting shoveling plate (15), wherein the wave-transparent rotary roller (16) is made of a microwave transparent material, the wall of the wave-transparent rotary roller is provided with a net-shaped or porous structure for fluid circulation, and the lifting shoveling plate (15) is fixed on the inner wall of the roller and is used for stirring and throwing materials in the rotating process.
2. The microwave synergistic supercritical fluid rotating bed devolatilization device for the polypropylene carbonate according to claim 1, wherein the front end of the exhaust valve (13) is provided with a high pressure difference resistant anti-blocking gas-solid filter (12) for preventing polymer dust from being carried out in the decompression process, the rear end of the exhaust valve (13) is connected with a vacuum pump (14), and the pore diameter of a net-shaped or porous structure on the wall of the wave-transparent rotating drum (16) is smaller than the minimum particle diameter of polypropylene carbonate particles to be treated.
3. A method for deep devolatilization of polypropylene carbonate using the apparatus of claim 1 or 2, comprising the steps of: S1, feeding and environmental replacement, namely opening a flange end cover, loading polypropylene carbonate particles to be treated into a wave-transparent rotary drum (16), locking the flange end cover, starting a magnetic coupling driving system to enable the wave-transparent rotary drum (16) to continuously rotate, vacuumizing or replacing gas in a high-pressure closed kettle body (6), and controlling the basic temperature in the kettle body to be 35-60 ℃ through a constant-temperature heating jacket; s2, performing multi-cycle variable-pressure cyclic devolatilization, wherein N times of cyclic operation are performed, and N is more than or equal to 2; S3, discharging, namely after the last circulation operation is completed, recovering the pressure in the kettle to normal pressure, and opening the flange end cover to take out the materials.
4. A method according to claim 3, characterized in that in step S2, the wave-transparent rotary drum (16) is kept continuously rotated in all process stages including pressure increasing, pressure maintaining microwave heating and pressure reducing, and the rotational speed is controlled to be 5-30 r/min.
5. The method according to claim 3, wherein in the step S2, the step of boosting is specifically that preheated carbon dioxide fluid is pumped into the kettle through an air inlet valve (17), so that the pressure in the kettle is raised from normal pressure or negative pressure to a high-pressure set value P 1 and maintained for 5-10 minutes, and the high-pressure set value P 1 is 8-30 MPa.
6. The method according to claim 3, wherein in the step S2, the pressure maintaining microwave heating step is specifically that a microwave heating system is started under the condition of maintaining the pressure P 1 in the kettle constant, the microwave power density is set to be 0.1-5.0W/g, the duration of the microwave is 10-120 minutes, and the polar impurities in the polymer are selectively heated by utilizing microwave energy to enable the polar impurities to be desorbed from the polymer chain segments.
7. The method according to claim 6, wherein in the pressure-maintaining microwave heating step, the microwave is in a pulse intermittent heating mode, the single microwave on time t on is set to be 10-300 seconds, and the stop time t off is set to be 10-300 seconds, and the microwave is alternately circulated.
8. The method according to claim 3, wherein in the step S2, the step of reducing the pressure in the single cycle is specifically that microwave heating is stopped, an exhaust valve (13) is opened to perform pressure relief, the pressure relief rate is controlled to be 5-30 MPa/min, the pressure in the kettle is reduced from P 1 to normal pressure, or after the pressure is reduced to normal pressure, a vacuum system is continuously started to vacuumize the kettle body, so that the pressure in the kettle reaches a negative pressure state.
9. A method according to claim 3, wherein in step S2, by periodically performing the pressure increasing step and the pressure decreasing step, the polymer particles are caused to generate an internal pressure gradient in the alternating change of swelling and shrinkage, and the mass transfer driving force between the solid phase and the gas phase is maintained by the gas phase displacement during each pressure decreasing.
10. The method according to claim 3, wherein in the step S1, the gas is replaced by introducing carbon dioxide, and in the step S3, the pressure in the kettle is restored to normal pressure by introducing carbon dioxide into the kettle.

Description

Microwave-assisted supercritical fluid rotating bed devolatilization device and method for polypropylene carbonate Technical Field The invention relates to the technical field of polymer processing, in particular to a microwave synergistic supercritical fluid rotating bed devolatilization device and method for polypropylene carbonate. Background Polypropylene Carbonate (PPC) is a typical aliphatic polycarbonate synthesized by copolymerizing carbon dioxide and propylene oxide as raw materials. As an environment-friendly completely biodegradable polymer material, the PPC has excellent gas barrier property, biocompatibility and transparency, has great application potential in the fields of fully degradable plastic bags, food packaging films, biomedical materials and the like, and is an important way for realizing the recycling of greenhouse gas carbon dioxide. During the synthesis, purification and subsequent processing of PPC, it is often necessary to use or inevitably leave a certain amount of unreacted monomers, reaction by-products and volatile organic solvents, among other impurities. If the residual solvents cannot be thoroughly removed, the residual solvents not only can seriously emit peculiar smell, so that the glass transition temperature and the mechanical strength of the material are greatly reduced, but also can directly limit the application of PPC in the fields of high added value such as food packaging, medical appliances and the like due to toxicity. Therefore, the deep devolatilization treatment of the PPC material is a necessary procedure for industrial production and high-end application. However, for deep devolatilization of high molecular polymers such as PPC, the conventional process faces a technical bottleneck which is difficult to overcome. The devolatilization methods commonly used in the industry today mainly rely on high temperature heat conduction to drive the volatilization. PPC is a typical heat sensitive polymer that has poor thermal stability and a low decomposition temperature. In the conventional high temperature devolatilization process, "zip" degradation or random chain scission is very likely to occur, resulting in a sharp decrease in molecular weight and material Huang Biancui. In addition, as the devolatilization process proceeds, the viscosity of the polymer system increases significantly, resulting in a substantial increase in mass transfer resistance within the liquid phase. At this time, the diffusion rate of the small molecular impurities from the inside of the material to the surface is remarkably reduced, and the small molecular impurities become a rate control step of the whole devolatilization process. In the traditional surface heating mode, although volatile components on the surface layer of the material can be removed quickly, the material is limited by huge diffusion resistance, and residual impurities in the deep inside are difficult to migrate to the surface. If the treatment temperature is increased or the heating time is prolonged in order to reduce the internal residual quantity, the thermal degradation of the PPC is inevitably aggravated, and the deep devolatilization is difficult to realize on the premise of ensuring the material performance. The prior art CN100506883C discloses an "aliphatic polycarbonate resin no-auxiliary agent devolatilization method and apparatus". According to the method, the resin melt is sequentially sent to the devolatilization tower and the exhaust type extruder for treatment, so that continuous devolatilization and granulation of the resin are effectively realized, the problem of solvent residue is solved to a certain extent, and a good industrial application effect is achieved. However, in order to maintain fluidity of the polymer melt and provide sufficient driving force for volatilization, the process generally requires that the operating temperature be controlled within the range of 130 ℃ to 220 ℃, and that the material undergo a certain residence time in the equipment. For polypropylene carbonates with extremely high thermal sensitivity, there is still a risk of inducing thermal degradation of the molecular chains in this high temperature environment in combination with the long thermal history of mechanical shearing. In summary, the existing devolatilization technology cannot efficiently and uniformly remove the residual solvent in the PPC at a lower temperature, and is difficult to solve the problem of adhesion and agglomeration of materials. Therefore, there is an urgent need in the art to develop a novel deep devolatilization process and apparatus that can achieve efficient mass transfer under mild conditions, avoid degradation of thermosensitive polymers, and effectively prevent material sticking. Therefore, the invention provides a microwave synergistic supercritical fluid rotating bed devolatilization device and method for polypropylene carbonate, which are used for solving the technical problems that the heat